This invention relates to devices for forming solder connections for example electrical connections between electrical conductors or mechanical connections between pipes and other equipment. In particular the invention relates to such devices that are dimensionally heat-recoverable.
Heat-recoverable articles are articles the dimensional configuration of which may be made substantially to change when subjected to heat treatment.
Usually these articles recover, on heating, towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In their most form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Pat. Nos. 2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage.
In the production of heat-recoverable articles, the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case maybe, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape.
In other articles, as described, for example in British Patent 1,440,524, an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating weakens and thus allows the elastomeric member to recover.
Heat-recoverable articles have become widely used for forming solder connections between electrical conductors in view of the ease of forming the connection and the quality of the connection so formed. For such applications the article, usually in the form of a sleeve, contains a quantity of solder for forming the electrical connection and a pair of fusible inserts for sealing the connection. These articles are described for example in U.S. Pat. Nos. 3,243,211, 4,282,396, 4,283,596, and 4,722,471, European Patent Publication No. 0,270,283, and British Patent No. 1,470,049 the disclosures of which are incorporated herein by reference, and are sold by Raychem Corporation, Menlo Park, Calif. under the trade mark "SOLDER SLEEVE" amongst others. Similar articles are also disclosed in U.S. Pat. Nos. 4,504,699 and 4,282,396, which disclosures are also incorporated herein by reference.
U.S. Pat. No. 4,722,471 discloses a solder connection device between a plurality of elongate bodies, which comprises a hollow, dimensionally heat-recoverable article having an aperture therein, the article containing a first solder insert for forming a solder connection between the bodies and containing a second solder insert, each insert being arranged to flow directly onto the bodies when the device is heated, the second insert being located adjacent to the first insert and responding to heat applied to the article more slowly than the first insert, so that, when the device is heated to form the connection, the second insert acts as a barrier to control the extent of flow of the fused first solder insert along at least one of the bodies.
European Patent Publication 0,270,283 discloses a device for forming a solder connection between a plurality of elongate bodies which comprises a hollow, dimensionally heat-recoverable article having an aperture therein, the article containing a solder insert for forming a solder connection between the bodies, and first and second heat-activatable inserts for environmentally sealing said aperture, said second adhesive insert having a higher viscosity than said first insert at the recovery temperature of the article, and being positioned with respect to the first insert to restrict the flow of the first insert under the recovery force of the article.
Although such devices are satisfactory for many applications, in certain unfavorable instances the quality of the environmental seal formed may depend on the skill of the installer, and, in particular, the devices may be sensitive to underheating or overheating or both. This may result in unreliable long term performance especially in corrosive environments or under severe mechanical stress, or damage to the sleeve of the device or the insulation surrounding the conductors to be connected.